The Study On Evaluation Of Turning Error Of Non-Rotationally Symmetric Optical Surface

NRS (Non-Rotationally Symmetric) optical surface have been widely used in security, aerospace, scientific research, as well as other areas in daily life for its advantages of optical properties and other advantages which the traditional rotary symmetric optical surface can not be achieved. A very high accuracy is required to the application of NRS optical surfaces, so, Ultra-precision machining of NRS optical surfaces is becoming the research hotspot. At the same time, the high-precision demand of NRS optical surface provides the testing and evaluation of NRS optical surfaces with a greater challenge. In addition, the development of Ultra-precision machining technology of NRS optical surfaces also requires higher accuracy in their testing and evaluation. This study aims to provide a high-precision testing and evaluation method for NRS optical surfaces, which can meet the accuracy requirements of NRS and has practicality and stability.The evaluation method of manufacture error of NRS optical surfaces is studied in this paper. The surface matching process is still using the popular step matching method.In pretargeting, the edge-pretargeting method is raised based on the current five-point positioning method and the SRS (Structured Region Signature) method, for the NRS optical surfaces which processed by diamond turning on tool servo platform are roughly circular. The orientation of the two surfaces are matched using the edge feature lines of the measured surface and design surface, and combined with the center of gravity and the best matched plane.Higher pre-positioning accuracy was eventually reached, and the matching process is adapted to NRS optical surface with a variety shape. The combination method of the least square method and the minimum area method is used in the fine adjustment algorithm. And the minimum area method has greater proportion. A pressing geometric iterative algorithm of the distance of the point outside of the surface to the surface is developed, laid the basis for fine adjustment process and achieve a high precision matching. The evaluation of circumferential direction and radial direction is used in the process of overall error evaluation. Thus the error evaluation standard becomes more comprehensive. For the error evaluation of the discrete points, this method uses the NURBS method to the reconstruction which is the current trend. It has more advantages other than B-spline surface reconstruction method such as higher accuracy and wider range of applications.To make the evaluation method of NRS optical surface more practical, a evaluation software of NRS optical surface has been developed in this papae. The software can be assessed on various NRS optical surface in the form of parametric equations or discrete points. At the same time, it has a friendly interface, complete functions, and has a simulation function.To validate the accuracy of the evaluation method, we carried out seveal simulation experiments on NRS optical surface in the form of parametric equations or discrete points, verified the accuracy and usefulness of evaluation algorithm and the software. To validate the practicality of the evaluation method further, we firstly designed software which can generat NC code automatically for diamond turning of NRS optical surface based on Slow Tool Servo. Then seveal NRS optical surfaces were processed with three-axis ultra-precision lathe. Secondly, we designed an In Place Detection method with three-axis ultra-precision lathe and laser micrometer, and examined the surface processed. Finally completed seveal actual experiments, verified the practicality of evaluation algorithm and the software.